1. Field of the Invention
This invention relates to a method for operating pumps, and more particularly to a method for stopping pumps in a pumping-up power plant having a single speed reversible pump turbine and a booster pump.
2. Description of the Prior Art
Generally, a single speed reversible pump turbine has such characteristics that the maximum efficiency point in the turbine operation mode is different from that in pump operation mode.
Namely, the turbine net head where the efficiency in turbine operation is maximum is larger than the pump total head where the efficiency in pump operation is maximum. But in a practical pumping-up power plant, the turbine net head in turbine operation is smaller than the pump total head in pump operation by the head loss of the water way between an upper reservoir and a lower reservoir. Therefore, when a pump turbine is operated as a turbine at a high efficiency speed or point, where the efficiency in pump operation is low, then it must be operated as a pump at a low efficiency point. Recently a new pumping-up power plant has been proposed where there is provided a booster pump in series with a single speed reversible pump turbine in order to prevent low efficiency in pump operation of the pump turbine. Namely, the booster pump is operated to provide a certain part of the necessary head for a high efficiency operation in the pumping-up power station in addition to the head generation by the pump turbine. As pumping-up power plants are confronted by a keen demand for high efficiency operation of the pump turbine from an economical standpoint, the demand for a method of operating a single speed reversible pump turbine together with a booster pump is very promising. But many technical problems arise in the operation of a single speed reversible pump turbine together with a booster pump, and an accurate control technique is necessary, especially in pump operation, for control in pump operation is very complicated.